The contactors of the state of the art comprise a coil arranged in a coil casing and configured for moving axially the mobile part of a magnetic core located in the center of the coil. The magnetic core is acting on a rod which controls a contact plate located outside of the coil casing in a contact chamber. The contact plate is destined for joining two electrical contacts having their ends in the contact chamber when the mobile part of the magnetic core is moved axially by the coil. The contact chamber is delimited by a cover through which the two electrical contacts are arranged. The cover is fastened to the coil casing. Furthermore, in order to ensure the isolation of the contact chamber in particular against humidity, a seal is needed between the cover and the coil casing. In the state of the art, the seal is made using a rubber seal which is positioned during assembly of the cover thanks to coil wires going through the cover. However, with such seal, there is a risk of deformation of the seal during transport (before assembly on the contactor) due to the flexibility of the material so that dedicated packaging needs to be foreseen leading to extra costs. Furthermore, the positioning of the seal is cumbersome and there is a risk of incorrect positioning which may lead to an isolation failure that may induce humidity to enter into the chamber and may cause lack of electrical contact due to the formation of ice on the contacts in low temperature. Ice is formed due to humidity condensation on terminals because of the temperature gradient induced by the accelerated cooling of the terminals with respect to the internal contact chamber temperature.